K  semileptonic BR measurement B. Sciascia 4 may 2006 KpmKSL joint meeting

1. K semileptonic BR measurement B. Sciascia 4 may 2006 KpmKSL joint meeting

2. Analysis scheme • Tag: Selection. 4 different samples are used. • Signal: Selection. Counting by means of a Fit procedure. • Efficiency: From MC. Data/MC corrections for Tracking, Track-to-Cluster, and Photon efficiencies. • Results: BR(Kp0en) and BR(Kp0mn) • Systematics: from Tag bias, FilFo, Cosmic veto/T3, Trigger, K nuclear interaction, Fiducial volume, Signal selection, and Efficiencies.

3. m- K- g K+ e+ g Signal selection Selection of K± semileptonic decays (Kl3) • 1-prong kaon decay vertex in the fiducial volume (40  rVTX  150 cm) • daughter track extrapol. to EMC • Reject two-body decays: • p(mp)  195 MeV • p0 search: 2 neutral clusters in EmC, with ToF matching the K decay vertex (d(dt)<3st) • Spectrum of charged daughter mass, m2lept, from TOF measurement: tdecayK = tlept -Llept /(bleptc) = tg-Lg/c • Fit m2lept spectrum with a linear combination of Ke3 and Km3 shapes, and background contribution.

4. Signal selection: m2 shapes • Signals and background have the same signature in m2. • Kpp0p0-with a p0 undergoing a Dalitz decay • Give a m2lept under the Ke3 peak. • Kpp0-with an early pmn- give a m2lept under the Km3 peak Km3 Ke3 Kpp0 K nucl.int. Kpp0p0

5. Background rejection-1 Kpp0, pmn Kp0en Kp0ln Kpp0p0 Kp0mn Kpp0p0 P(MeV) Emiss-Pmiss (MeV) • Kpp0 events are rejected evaluating the missing momentum at the decay vertex, and cutting on momentum of the secondary track in the Pmiss rest frame (P>80 MeV) • Kpp0p0 are rejected cutting on Emiss-Pmiss spectrum (<90MeV); the p0 momentum is obtained by mean of a kinematic fit

6. Signal selection: m2 final shapes • The previous cuts reject about 96% of background events • The efficiency on the signal is: about 55% for both Ke3 and Km3 Kpp0p0 Kpp0 K nucl.int. • The residual background is about 1.5% of the selected Kl3 sample, and has the mp2 signature.

7. The ingredients of the measure Fiducial volume efficiency 58% Tag bias correction, from MC Fit results N(Kl3) 11 (eTAG(i) BR(i)) aCF BR(Kl3) = NTAG(1-fNI)eFVeSELEeTAG(Kl3) Cosmic veto/T3 and FilFo correction to the Tag bias, from Data and MC 4 tag samples K nuclear interaction correction About 9% for each sample e(KINK)DATAe(TCA)DATA e(p0)DATA   eSELE= eSELE_MC e(KINK) MCe(TCA) MC e(p0) MC

8. What’s new Tracking efficiency correction: Dependency on lepton momentum, studied in 2 samples. - Kl3 enriched vs (Kt’,Kp2) enriched Systematics of the correction from difference of control samples. Signal selection: Good stability wrt selection cuts and tracking variables fNI: Kaon nuclear interaction measured directly on data Small disagreement MC-Data Correction applied to N(K-) + rescale TB

9. BR measurement (almost final) • All contributions to the error are included. Some checks “of completeness” are still needed. • “1-e” include syst. from tag and fit counting (0.02-0.04%) • Final error dominated by uncertainty on the efficiency correction (essentially TRK, poor statistics). • Syst from tracking calculated and applied “per charge” (not “per tag”): 0.02% absolute

10. Conclusions • Difference wrt the blessing: essentially due to the previous lack of momentum dependency in the tracking efficiency correction. • Important check of negative kaon nuclear interactions, poorly known at pK 100 MeV • Playing with Vus (thanks to MM) • VUSf+(0) value: from 0.21671(48) to .21699(50) • “big” fractional errors: Ke3 at 1.5% and Km3 at 2.5% level. • c2 of KLOE measurements: 7.7/4 (Prob10%); before was 2.3/4. • Good agreement with E865 result (…also with rumors from NA48, MA). • ? ---- Appreciable difference between charged and neutral estimations ----? • Blessing of the final result ready in few weeks

11. Counting of the events (new) Number of events selected for each signal divided per tag: • Tag • Signal from the fit • Correlation matrix from the fit:

12. Counting of the events (old) Number of events selected for each signal divided per tag: • Tag • Signal from the fit • Correlation matrix from the fit:

13. Tag K+m2 Tag K+p2 Tag K-m2 Tag K-p2 Absolute BR(Ke3(g)) measurement • Uncorrelated errors between the 4 tag samples: Nsig, tag bias, FilFo, CosmicVeto/T3, MC stat. used for efficiency evaluation, photon efficiency. • Partially correlated error: kink and TCA efficiency corrections of MC efficiency. • c2/nDof = 3.20/3 for the 4 measurements with uncorrelated errors, P(c2> cM2)  36%

14. Tag K+m2 Tag K+p2 Tag K-m2 Tag K-p2 Absolute BR(Km3(g)) measurements • c2/nDof = 5.32/3 for the 4 measurements with uncorrelated errors, P(c2> cM2)  15% • The number of signal events is evaluated in each sample separately, using the SAME FIT PROCEDURE.Systematic errors coming from the fit are common to all samples. • Also the systematic coming from the selection efficiency is COMMON TO ALL SAMPLES.

15. Tag K+m2 Tag K+m2 Tag K+p2 Tag K+p2 Tag K-m2 Tag K-m2 Tag K-p2 Tag K-p2 Kℓ3 - Results • The error accounts for the data and Monte Carlo statistics used in the fit, the MC statistics for the efficiency estimation, the Data/MC efficiency corrections, and the systematics on the tag selection. • The systematics due to the signal selection efficiency is under evaluation. • c2/nDof for the 4 measurements: • Ke3: 3.20/3, P(c2> cM2)  36% • Km3: 5.32/3, P(c2> cM2)  15% • Averages carefully calculated taking correlations into account: KLOE preliminary • The error is dominated by the error on Data/MC efficiency correction. • Fractional accuracy of 0.9% for Ke3, 1.2% for Km3.